How do you make homemade low carb sausages?

The only low carb sausages I can buy locally are the M&S 95% ones which are nice but a bit pricey, especially as the nearest M&S is 10 miles away. My BIL bought us a mincer with sausage-maker attachment so I thought I would try making my own.

I have bought some hog casings and a gluten-free seasoning pack which has potato instead of breadcrumbs but I'm wondering what meat would be best to make low carb - high fat sausages. I think a combination of pork belly and pork shoulder would work but I'm not sure of the proportions. Has anyone tried making their own low carb sausages.